[quote][b]Posted by:[/b] DarkestSeptagon
There's probably a universal time that everyone follows. Then there's a colonies own time system, for like business and government. That's just how I think it works.[/quote]

If you notice in the novels, at the beginning of every chapter they specify the date and time of the military calendar. I'm assuming the military calendar is similar to zulu (Greenwich Mean Time) time used in the military today.
Also, local time is used in some cases. In the sniper mission on reach, you can see that its 2600 hours or so, suggesting that a day on reach is at least 2 hours longer than one on earth.
[Edited on 10.19.2012 9:21 AM PDT]